1. Field of the Invention
The present invention relates to an apparatus and method for polishing substrates. More particularly, the invention relates to the control of slurry delivery to a polishing pad.
2. Background of the Related Art
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited and removed from a substrate during the fabrication process. Often it is necessary to polish a surface of a substrate to remove high topography, surface defects, scratches or embedded particles. One polishing process is known as chemical mechanical polishing (CMP) and is used to improve the quality and reliability of the electronic devices formed on substrates. An exemplary polishing system used to perform CMP is the Mirra(copyright) System available from Applied Materials, Inc., as shown and described in U.S. Pat. No. 5,738,574, entitled, xe2x80x9cContinuous Processing System for Chemical Mechanical Polishing,xe2x80x9d the entirety of which is incorporated herein by reference.
Typically, the polishing process involves the introduction of a chemical slurry during the polishing process to facilitate higher removal rates and selectivity between films on the substrate surface. In general, the polishing process involves holding a substrate against a polishing pad under controlled pressure, temperature and rotational velocity of the pad in the presence of a slurry or other fluid medium. The slurry is primarily used to enhance the material removal rate of selected materials from the substrate surface. As a fixed volume of slurry in contact with the substrate reacts with the selected materials on the substrate surface, the slurry constituents are consumed. Accordingly, the slurry becomes less reactive and the polishing enhancing characteristics of the slurry are significantly reduced.
In an attempt to ensure a substantially constant and uniform removal rate of material from the substrate being polished, conventional methods continually supply large volumes of slurry to the pad during a polishing cycle. As a result, slurry is the primary consumable in chemical mechanical polishing and a significant source of the cost of operation. In order to minimize the cost of operation, the volume of slurry used in a processing cycle should be minimized.
Therefore, there is a need for a method of polishing a substrate while minimizing the volume of slurry consumed.
The present invention generally provides an apparatus and method for polishing a substrate which improves the delivery of slurry over the surface of a polishing pad while providing uniformity and planarity of the polishing process. The method is preferably adapted for incorporation into a chemical mechanical polishing system.
In one aspect of the invention, a polishing assembly is provided having a polishing pad and a fluid supply system including a fluid delivery arm and a fluid delivery module. The fluid delivery arm disposed near the polishing pad includes one or more delivery lines and at least one slurry delivery line. The fluid delivery module is coupled to the fluid delivery line and is adapted to regulate the flow of slurry during a polishing cycle. The fluid delivery module may include one or more of flow control valves, controllers and microprocessors used alone or in combination to control the rate at which slurry is delivered to the polishing pad.
In another aspect of the invention, a method of varying the rate of slurry flow onto a pad during polishing is provided. The method comprises flowing a fluid from a fluid delivery source while varying the flow rate of the fluid.
In yet another aspect of the invention, a method of polishing a substrate is provided. The method comprises positioning a substrate in contract with a polishing pad and supplying a fluid onto the pad while periodically varying the rate of fluid flow onto a pad. In one embodiment, the fluid flow may be continuous while the rate is varied or, alternatively, the fluid flow may be periodic so that fluid flow is turned OFF and ON.
In yet another aspect of the invention, a method of varying the rate of fluid flow onto a pad during polishing is provided. The method comprises providing a fluid delivery line adjacent a polishing pad, providing a slurry source coupled to the fluid delivery line, flowing a slurry from a slurry source through the fluid delivery line and onto the polishing pad, and varying the flow rate of the slurry out of the fluid delivery line and onto the polishing pad. In one embodiment, the fluid flow may be continuous while the rate is varied or, alternatively, the fluid flow may be periodic so that fluid flow is turned OFF and ON.
In still another aspect of the invention, a signal-bearing machine-readable medium includes a program which, when executed on the computer system, controls the fluid flow to a CMP system during processing. One embodiment of the program is adapted to utilize user-selected values for the rate of the fluid flow. Additionally or alternatively, an embodiment of the program is adapted to provide a continuous fluid flow while the rate is varied or, alternatively, a periodic fluid flow so that fluid flow is turned OFF and ON.
In still another aspect of the invention, a polishing system comprises one or more rotatable platens, a polishing pad disposed on each of the rotatable platens, a fluid supply system including a fluid source and a fluid delivery arm coupled thereto, and a computer system coupled at least to the fluid supply system and adapted to vary the flow rate of a fluid from the fluid delivery arm onto the polishing pad during a polishing cycle.